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9.7 Landsats 4, 5, 6. and 7

Landsats 4, 5 (and 6) carried, in addition to the MSS, a new instrument called the Thematic Mapper. Here are an artist's sketch of the Landsat 4 spacecraft and a drawing with labeled components, which point to the notable differences from the previous Landsats.

A new 7 spectral band scanner, called the Thematic Mapper, was/is the prime instrument on Landsats 4, 5, and 6. This improved sensor system includes a blue band so that quasi-natural color images can be made, two bands in the mid-IR, and a thermal band. System resolution is increased to 30 meters. Landsat 7 carried a single sensor, the ETM+, which has a panchromatic band that achieves 15 m resolution. The TM identify better materials and classes.

Landsat 7 mounts only a single payload, the Enhanced Thematic Mapper (ETM+). The ETM+ includes not only the 7 TM bands (the thermal band [6] has 60 m resolution), but also a panchromatic band that is capable of 15 m resolution. This artist's rendition shows that the spacecraft differs in general construction from the previous "birds".

For full scenes printed at a scale of 1:1,000,000 (the standard product, about 10 inches on a side, with white margins), the TM and MSS products show strong similarities, even in the details. This is because the effects of the added pixels (representing areas on the ground) at 30 meters do not appear sharply different in the TM images when compared with the 79 meters of the MSS. For an image of this scale, which extends over 7 inches on a side, for the 79 meter case, the size of a pixel is 79/185000 x 7 = 0.003 inches (the 185000 refers to the ground equivalent length of 185 km for the scene). The 30 meter case gives a pixel size of 0.001 inches. The eye cannot clearly differentiate between these two sizes.Where the higher resolution TM image produces obvious improvement occurs when the scale is changed to larger sizes (1:250,000 produces a 28 inch wide full image), with the pixels remaining still small enough (0.004 inches) not to be distracting to the eye (but the 79 meter MSS would have pixels of 0.012 inches, so that pixels will be seen and give a tiny but disturbing blocky effect). Likewise, when a sub scene (part of a full image) is produced from TM data, it also appears sharper when printed at some typical size (e.g., 10 inches).

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h's surface more as classes than as materials per se. Consider, for instance, the material concrete. We us it in roadways, parking lots, swimming pools, buildings, and other structural units, each of which might be treated as a separate class. We can subdivide vegetation in a variety of ways: trees, crops, grasslands, lake bloom algae, etc. Finer subdivisions are permissible, by classifying trees as deciduous or evergreen, or deciduous trees into oak, maple, hickory, poplar, etc.